This study proposes to characterize the pathophysiology and course of glomerular injury in patients with different types of glomerulopathies. The investigators hypothesize that alterations in the glomerular capillary wall (GCW) pore-size structure (loss of pore density and changes in pore size distribution) are the ultimate cause of hypofiltration and proteinuria, and that progressive azotemia is the result of progressive injury to the GCW itself. Seventy patients are planned for study, and 20 have already been completed.